Separation of aliphatic acids



United States Patent Q 3,002,018 A SEPARATION OF ALIPHATIC ACIDS Funston G. Lum, Richmond, Califl, assignorto Cali-. forma Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing Filed Sept-22,1958, Ser. No, 762,212 4 Claims. cram-s37 This invention relates to a separating in the form of their full salts straight chain aliphatic dibasic acids from'their branched chain isomers and more particularly-to a novel method for removing pure sebacic acid from reactionmixtures containing sebaeioacid, isomeric C acids,,such as,2,2 f-diethyl adipic acid and 2-ethyl suberic acid, as well, certain C -C monobasic acids. I I

US; Patent 2,749,364 discloses a method for the re; covery of C aliphatic dibasic acids from mixtures of salts of sebacic acid and other isomeric G acids, together withsmall; amounts of. other acids, including monobasic carboxylic; acidsobtained by=- carbonation landv hydrogenation of, the dimetalloproducts; formed by treatmg butadiene with finely dispersed, sodium -,or.potassium in a selectedether medium in the, pr sence of a relai ys a l mo nt o po y ycl aroma ic. y ro arbons and/or a solid attrition, agent at a temperature prefer,- ably below C. These C dicarboxylic acids are obtained in the form of the full alkali metal salts, that is, salts in which-both hydrogens of the acid groups have been replaced by an alkali metal cation, the term alkali metal cationalso embracing the ammonium cation, as distinguished from the half oracidsalt referred;;-toas such.

In the practice of the aforesaid patent whenn using sodium as the metal, a typical mixture compriseslthe Cm dicarboxylic acids in the form of the sodium salts, sodium salts of various monobasic C and C acids, small. traces of hydrogenation. catalysts, condensed polymeric acids, and about 15% sodiumchloride. Further, in. accordance withtheteaching ofthat patent, benzene is added to. the, mixture in an,.-amount,about equal to 20% of the total volume .of thetaqueous. reaction. mixture, followed by addition of concentrated hydrochloricacid in amounts varyingbetween 5 and .l0 by volume of the aqueous vmixture .tosthe mixtureuso as to form the monosodium salts of sebacic acid and the isomeric, C acidproduct. The solution is then saturated. with sodiumnchloride, whereuponthereare formed a solid phase ofmonosodium sebacate and. a liquid phase, havingthe monosodium isomeric C acids andv the other. impurities, concentrated, respectively, in the, aqueous and benzenelayersthereof, A mixture of theisomeric C acids is late separatedfrom the. aqueous. layer. of the liquid phase, the composition of the mixture, known as isosebacic acid, being approximately,

Percent process for isolating and Sebacid acid Z-ethyl suberic acid 72450 The method of separation describedin theaforesaid patent suffers from certain, disadvantages which this invention is designed to remedy, The, first disadvantage is the necessity of converting thealkal i metal salts of sebacic, acid and the, isomeric C acids to the monoalkali metalIsalts, which requires initial accurate determination of the free alkali and total organic acidcontent. and then controlled addition. of mineral. acid to convert full salts to the half salts. A second, andmore important disadvantage in the prior artmethpd, is the fact, that the separations are incomplete. Although substantially pure sebacic acidcan be obtained, a consider- 6,- 2,2'-diethyl adipic acid--- 12-18 Win- (at ice ahle amount of thesebacic acid originally present in. the reaction mixture is. notrecovered but is found inithe. isosebacic acid.- Sebacic acid is commercially more valuable than the isosebacic acid, and as a result, as complete areeoyery of sebacic acid as possible is strongly desired. Furthermore, in the event it is desired to separate the .2,2'-diethyl adipic acid from the Z-ethyl suberic acid, which are bot h contained in the isosebacic acid mixture, it is advantageous to eitect suchseparation in theabsenceof sebacic acid contaminant, which being presentmakesthe separation of the other fractions more diificult.

ord sly n, o e t at. e. p sntn v ntion. i to p vi a proc s r ffect e ar tions. as a nev Po on ontains. ub ta i l y P s lt c mada the other portion contains a mixture of various iso meric C acids substantially free from thepresence of ehas e idf, l

lt has been disco vered that the alkali metal salts of sebacic acid'are substantially completely insoluble in concentrated and saturatedv aqueous solutions of the same liii i M l?! sa ts f-i fi C10 s e 19 P 't mix res. om oses, m l'y of 2 2'- i thy i1 acid and Z-ethyl suber i'c acid. This is surprising, inasmuch asthe alkali metal salts of sebacic acid are quite soluble in water alone. I I

Based on the foregoing discovery of the insolubility of the alkali metal sheet sebacic acid in the same alkali metal salts of isomeric C acids, a process for separation of mixtures of these salts has been developed which comprises forming an intimate mixture of these salts with-a quantity of water insufficient to dissolve all of the salts but fully sufficient to dissolve all of the alkali metal salts. of the isomeric C acids, separating a solid phaseand-a liquid phase, regeneratingpure sebacic acid from the solid phase, and regenerating isomericC acids from the liquid phase. The methodsis peculiar to the separation of sebacic acid from itsisomers. For example,.it has been. attempted experimentally to separate 2,2-diethyl adipic acid from Z-ethyl suberic acid by means of the methods employed in this invention. Sucha separation has proved to be totally ineffective.

The method of forming the separable mixtureis not critical.- For example, one method that may be used to form a separable mixture is to dissolve in water a mixture of the alkali metal salts of sebacic acid and the isomeric C acids so as to form a homogeneous solution. The solution is then evaporated until it contains about 40 to 70% by weight of the :alkalimetal salts of the isomeric C acids. At the higherconcentrations, substantially all of the alkali metal sebacate present isfully precipitated. The precipitate is then separated from the mother liquor by conventional means such as by filtration, decantation,

.centrifuging and the like. The precipitate is their washed with small portions of a saturated solution of an inorganic salt of the same alkali metal with higher molar solubility than the sebacate to remove any alkali metal salts of the isO lertic acids which may cling to it, If desired, a water miscible alcohol or its water mixture may be employed in place of the saturated salt solution as a wash. The amount of water in such alcohol Water mixtures should be kept low so that the solvency forethe sebacate salt is poor.

The initial filtrate is combined with the Washes, and a mixture of isomeric, C acids substantially free of sebacic acid can be recovered by conventional means.

If the acids themselves ratherlthan the alkali metal salts are available, they can'be neutralized with a volume of alkali metal base, such as sodium, ammonium, or potassium hydroxide, suflicient to form the alkali metal salts and the separation process then carried out as indicated above.

If the alkali metal salts of sebacic acid and the isomeric C acids are present as solids, a more convenient manner in which to make the separation is to add the mixture of salts to a volume of water insuflicient to dissolve the alkali metal salt of the sebacic acid but fully sufiicient to dissolve all of the isomeric C acids. The salts are added with stirring and a separation is eifected. For the sodium salts, this complete separation occurs when the mother liquor contains approximately 40% or higher of the isomeric C acids by weight. With the potassium and ammonium salts slightly higher concentrations are necessary to effect substantially complete separation.

The separation proceeds quite smoothly at room temperatures, although any convenient temperature range may be employed. At higher temperatures, the separation has to be carried out at higher salt concentrations because of their increased solubilities.

This invention can better be illustrated by the following examples, which, however, are not meant to limit it:

Example I A mixture having the following composition was prepared by neutralizing commercial isosebacic acid with aqueous sodium hydroxide:

Percent by weight Sodium isosebacate 41 Water 59 The undissolved sodium sebacate was separated by filtration and washed three times with saturated sodium chloride in the ratio of about four parts by weight of saturated sodium chloride per part of sodium sebacate. The washes were added to the original filtrate for recovering the isomeric C acids. The filter cake was dissolved in water and the sebacic acid regenerated upon acidification with hydrochloric acid. The sebacic acid was filtered,

washed with water, and dried. The amount of sebacic acid recovered amounted to approximately 80% of sebacic acid present in the original isosebacic.

Example 11 Example III In this example, the potassium salts were employed in place of the sodium salts. The potassium isosebacate content of the mixture prepared was 62%. In this case, the separated potassium sebacate was washed with a :1 isopropanol-water mixture instead of with a saturated aqueous solution of a highly soluble inorganic potassium salt. The recovered sebacic acid amounted to about 70% of the sebacic acid present in original isosebacic acid. More complete separation is possible as indicated by further precipitation upon concentrating the original mother liquor.

Example IV In this example, the ammonium salts were employed. The ammonium isosebacate content of the mixture used was about 70%. As with Example III, a mixture of 5:1 isopropanol-water was used as the wash. The recovered sebacic acid in this example amounted to about 80% of the sebacic acid present in the original isosebacic acid. More complete separation is possible as indicated by further precipitation upon concentrating the original mother liquor.

In the above four examples, commercial isosebacic acid in commercial isosebacic illustrate this point.

Example V A mixture having the following composition was prepared by neutralizing the acids with aqueous sodium hydroxide:

Percent by weight Sodium sebacate 12 Sodium 2-ethyl suberate and 2,2'-diethy1 adipate 28 Water 60 The solution was concentrated by evaporation to the following composition:

Sodium seb cate 18.5 Sodium 2-ethyl suberate and 2,2."diethy1 adipate--- 43 Water 38.5

The mixed C acids having the same composition used in Example V was neutralized with aqueous potassium hydroxide to give a mixture having the following composition:

Percent by weight Potassium seb 15 Potassium Z-ethyl suberate and 2,2'-dicthyl adipate 35 Water 50 The solution was concentrated by evaporation to the following composition:

The undissolved potassium sebacate was separated by filtration and washed with a 10:1 isopropanol-water mixture. The sebacic acid was regenerated as described in Example I. The yield of sebacic acid showed that ap proximately of the sebacic acid was recovered.

I claim:

1. Process for recovering sebacic acid from isosebacic acid which comprises concentrating an aqueous solution of the full alkali metal salt of isosebacic acid to precipi tate the full alkali metal salt of sebacic acid but discontinuing the concentration before the precipitation of the full alkali metal salt of the isomers of sebacic acid contained in the isosebacic acid, separating the precipitate from the liquid phase and regenerating sebacic acid from the precipitate.

2. Process according to claim 1 wherein the alkali metal is sodium.

3. Process for separating a full alkali metal salt of sebacic acid from the full alkali metal salt of isosebacic acid, which comprises mixing the full alkali metal salt of isosebacic acid with an amount of water sufficient to dissolve substantially all of the full alkali metal salts of the isomers of sebacic acidcontained in the isosebacic acid salt but insufiicient to dissolve a substantial quantity of the full alkali metal salt of sebacic acid, and separating the undissolved full alkali metal salt of sebacic acid from the dissolved salt.

4. Process according to claim 3, wherein the alkali metal is sodium.

References Cited in the file of this patent Noller: Chemistry of Organic Compounds, 2nd edition, page 794. 

1. PROCESS FOR RECOVERING SEBACIC ACID FROM "ISOSEBACIC ACID" WHICH COMPRISES CONCENTRATING AN AQUEOUS SOLUTION OF THE FULL ALKALI METAL SALT OF "ISOSEBACIC ACID" TO PRECIPITATE THE FULL ALKALI METAL SALT OF SEBACIC ACID BUT DISCONTINUING THE CONCENTRATION BEFORE THE PRECIPITATION OF THE FULL ALKALI METAL SALT OF THE ISOMERS OF SEBACIC ACID CONTAINED IN THE "ISOSEBACIC ACID," SEPARATING THE PRECIPITATE FROM THE LIQUID PHASE AND REGENERATING SEBACIC ACID FROM THE PRECIPITATE. 